(Naval.txt)
A PROPOSED NAVAL STUDY:
THE ANNAPOLIS
PILOT VISION MAINTENANCE
PROGRAM
A Preventive Proposal
for
THE UNITED STATES NAVAL ACADEMY
Otis S. Brown
General Electric, Space Division
Goddard Space Flight Center
Greenbelt, Maryland 20771
Dr. Peter R. Greene
Department of Biomedical Engineering
Homewood Campus
THE JOHNS HOPKINS UNIVERSITY
Baltimore, Maryland 21218
THE ANNAPOLIS PILOT VISION MAINTENANCE PROGRAM
This proposal is dedicated to the Midshipman's right to make
a decision regarding myopia avoidance.
Topics for Discussion
1. Abstract
2. Background
3. Objectives
4. The Prevention Technique
5. Cockpit Myopia
6. Specific Instructions to the Midshipman
7. A Dichotomy in Eye Research and Method of Practice
8. The Right of the Midshipman to make a Decision Regarding
Nearsightedness Avoidance
9. Scientific Rigor Vs. The Midshipman's Right to Know and
Choose
10. The Placebo Summary
11. The Group Affected
12. The Cost of the Program
13. The Principal Investigator
14. Two Theories of the Eye's Focal Growth
15. Scientific Measurement
17. Summary
16. A Physiological Model for Demonstration
18. References
THE ANNAPOLIS PILOT VISION MAINTENANCE PROGRAM
ABSTRACT
The Naval Academy requires 20/20 vision for admission of
freshmen. Prospective pilots are required to have 20/20 vision on
graduation from the Academy. A substantial number of midshipmen,
entering with 20/20, become nearsighted during their four years of
study at the Academy.
An engineering analysis of the eye's control action predicts
that a large percentage of the midshipmen could -- in fact --
avoid the problem if they wear convex lenses while reading. This
analysis is supported by direct experimental evidence. (l) (2)
BACKGROUND
20/20 does not fully define the eye's focal status. A more
meaningful measure is a quality described as "hyperopic reserve".
The quality is easily measured with an eye chart and a positive
(convex) lens. In a study at the Naval Academy, conducted by Dr.
Hayden, it was determined that the confined (reading) environment
resulted in a steady movement towards and into myopia. (3) This
movement towards nearsightedness is not measured in the eyes of
primitive (Eskimo) men. (4)
If the visual environment of the midshipmen is changed from a
near environment to a "far" environment by use of a positive lens
for reading, the movement towards myopia will stop, and the
midshipmen will avoid the problem of myopia. (5)
OBJECTIVES
The major objective of the proposed program is to demonstrate
that midshipmen, who are on the verge of becoming nearsighted,
(zero diopters hyperopic reserve) will completely avoid the
problem. It has been documented that military cadets will develop
approximately 1.3 diopters of nearsightedness after four years at
the West Point Military Academy, if no preventative action is
taken. (7)
The objective of the prevention technique is to demonstrate
that at least half of the midshipmen who assiduously wear the plus
lens will avoid becoming myopic during their four years at the
academy. The 50% figure is a minimum acceptable performance
figure -- the actual results should be considerably better.
THE PREVENTION TECHNIQUE
The reading (confined) visual environment can be neutralized
by a positive lens. The convex lens makes diverging rays of light
parallel, thus simulating the effect of a "distant" visual
environment. The eye's internal lens is thereby adjusted to
infinity, rather than the actual near-by object.
The specific lens strength chosen will be determined by the
midshipman's habitual reading distance. For instance, if the
habitual reading distance is 20 inches, a lens with focal length
of 23 inches (+ 1.75 diopters) will neutralize most of the "near"
visual environment. Obviously, habitual reading distance
determines the selection of the convex lens strength.
A POSITIVE LENS MAKES DIVERGING RAYS OF LIGHT PARALLEL
THUS SIMULATING A DISTANT OBJECT FOR THE EYE
COCKPIT MYOPIA
The wearing of a convex lens for reading will have one
immediate beneficial effect - - the ending of the problem of
cockpit myopia. This condition occurs after prolonged close work.
When the individual looks up, distant objects are blurred, and it
can take a considerable amount of time before distant objects
become clear again.
By wearing a positive lens for all close work, the
accommodation system is already set at infinity, and the eye will
be in immediate clear focus for distant objects, thus completely
ending this particular problem.
SPECIFIC INSTRUCTIONS TO THE MIDSHIPMAN
Once the positive lens is chosen, the Midshipman must be
instructed to push his reading material away from his eyes until
the work blurs -- accommodation set at infinity -- and then move
the work inward slightly. This procedure will effectively place
the reading material at infinity, so that the positive lens will
have the maximum neutralization effect. If he does not do this,
he may inadvertently hold his work somewhat closer than necessary
-- which will partially negate the effeect of the positive lens.
THE DICHOTOMY IN EYE RESEARCH AND METHOD OF PRACTICE
There are two major opinions held by the eye care profession.
They are:
1. The Negative-lens Theory: The visual environment and/or lens
has absolutely no effect on the focal status of the normal
eye.
2. The Dynamic Theory: Both the visual environment and/or a lens
have a direct bearing on the eye's focal status. The eye
continually sets its long-term focus by reference to the
average value of accommodation.
These two contradictory opinions result in two contradictory
methods of practice.
1. The eye becomes nearsighted -- not because of a near
environment --but by pure genetic cause. Since this factor
makes nearsightedness incurable, no attempt should be made to
solve the problem, and when the eye fails the eye chart, a
negative lens must be prescribed.
2. The preventative (positive lens) technique advocates
nearsightedness avoidance by neutralizing the effect of a
confined visual environment. This technique -- or some
variant -- is used by 20% of the eye care profession.
Nearsighted avoidance (and recovery) is a recognized
technique that is established by the fact that it is practiced by
20 percent of the profession.
THE RIGHT OF THE MIDSHIPMAN TO MAKE A DECISION REGARDING
NEARSIGHTEDNESS AVOIDANCE
Since midshipmen with hyperopic reserve of 0 to + 0.25
diopters will become nearsighted one or two years after
matriculation, it follows that the midshipmen who wish to enter
Naval Air on graduation should be given the opportunity to make
the decision to avoid becoming myopic by use of the positive lens
technique.
The visual records of the incoming class should be culled for
visual focal status from 0 to + 0.5 diopters, Those individuals in
this group shall be informed of their right to make this decision.
Once the decision is made by the midshipman, his focal status
shall be monitored to verify the effectiveness of the preventative
technique.
SCIENTIFIC RIGOR VERSUS THE MIDSHIPMAN'S RIGHT TO KNOWN AND
CHOOSE
The major purpose of this study is to provide the midshipman
with the opportunity to avoid myopia. A further purpose is to
provide him with the supporting focal status measurements obtained
from his own eyes, to validate the effectiveness of the technique.
To carry out the preventative technique, the cadet must be
given information regarding the characteristics of a plus and
minus lens -- and the expected results of these two techniques.
The availability of this information will preclude the use of
placebo (plate glass) group, since the placebo group will quickly
become aware that their lens can have no effect on their
developing case of nearsightedness.
Not all of the 300 midshipmen who are in imminent danger of
becoming nearsighted will wish to be part of the preventative
group. This group will be the control group. This group will
only establish a fact that is already known -- that if you do
nothing, your focal status will move towards nearsightedness at
the rate of 1/3 diopters per year. (3)
THE PLACEBO SUMMARY
The right of the midshipman to know and to choose is more
important than the need for a placebo group. The standard rate of
focal change (-.33 diopters per year) is an already known value.
The placebo group would interfere with our ability to provide
information about the use of the plus lens -- which is essential
for the success of the project. The midshipmen who are not part
of the preventative program will serve as the placebo group.
THE GROUP AFFECTED
The Naval Academy accepts 1,000 freshmen per year with 20/20
vision. This group has an approximately gaussian distribution of
hyperopic reserve -- from 0 to +2.0 diopters. Approximately 30%
of this group will have hyperopic reserve of from 0 to +.5
diopters. (i.e. They are on the edge of nearsightedness.) Almost
all midshipmen in this group will become nearsighted if nothing is
done. This fact is confirmed by a previous measurement study
conducted at the Naval Academy. (3)
This group will be identified from their visual records, and
will be given the opportunity to join the myopia avoidance effort.
THE COST OF THE PROGRAM
The preventative (positive) lens is relatively inexpensive,
since it is a "standard" item available in larger drug stores for
about $8. The initial outlay is relatively modest to support the
program. In addition, these lenses need not be changed for the 5
years of the program. The midshipmen who avoid nearsightedness by
the prevention technique, will also avoid the expense of
prescription ground lenses which typically sell for $40, and are
changed every one or two years. The prevention technique will
result in a considerable dollar saving for the Naval Academy.
THE PRINCIPAL INVESTIGATOR
Dr. Karel Montor; Director, Division of Applied Sciences,
USNA, is conversant with this proposal. We recommend that he be
asked to serve as the principal investigator.
TWO THEORIES OF THE EYE'S FOCAL GROWTH
Nearsightedness is a medical problem, but it points to a much
broader scientific question: "How does the human eye achieve and
sustain a high level of focal accuracy?" There are only two
possible explanations.
1. The Negative-lens Theory: The eye's long-term focus is
genetically controlled. All optical components are
pre-determined from birth.
2. The Dynamic Theory: The eye is subject to continuous focal
micro-perturbations. The effect of these perturbations is to
randomize the eye's focal status. The eye has a long-term
focal control system which is directed by the accommodation
system. Only the existence of a focal dynamic system can
account for the high level of accuracy seen in the human and
primate eye.
These two theories are reasonable, but they lead to
predictions that are directly contradictory. A scientific
approach calls for the testing of two theories by direct
experimentation,
Dr. Francis Young has carried out a visual environment test
on monkeys. A theoretical review of this experiment demonstrates
that the predictions of a dynamic theory are an order of magnitude
more accurate than the negative-lens theory. (2)
The theory that has the greater predictive accuracy
ultimately becomes the preferred theory for scientific research.
Once initial confirmation is obtained, effective analysis of the
eye can be obtained by use of a dynamic control theory.
SCIENTIFIC MEASUREMENT
The eye responds to the environment (6). The eye's focal
status will, necessarily, move towards nearsightedness if placed
in a confined visual environment. The purpose of the plus lens is
to substantially alter the eye's average value of accommodation.
The equation which relates the average value of accommodation to
the eye's focal status is:
Focus = Focus + ( Offset + Accommodation - Focus ) - Perturbation
----------------------------------
TAU
(This is an iterative equation)
The required parameter for this equation is the eye's average
value of accommodation on a daily basis. Since the midshipman is
mature enough to monitor his usage of a plus lens, we can ask him
to estimate:
1. The number of hours per day that he spends looking at distant
objects. (i.e. Athletics)
2. The number of hours he spends doing close work, and the number
of hours he actually used the plus lens to neutralize the
confined visual environment.
To calculate the eye's focal status we need to know:
1. The distance he holds his reading material from his eyes, and
the strength of the plus lens.
2. The number of hours he uses the reading glass for close work.
From this supplied information we will calculate:
1. The midshipman's average visual environment.
2. The midshipman's visual environment if he had not worn the
plus lens.
By use of the piecewise (iterative) equation we may then
predict his eye's focal status, and compare the measured focal
status against the predicted focal status.
It should be clearly understood that the predictions of the
iterative equation have previously been confirmed by direct
experimental work with monkeys. (l) (2)
SUMMARY
Nearsightedness prevention is a difficult problem. It will
take a major commitment to carry out an effective prevention
program, testing whether the negative-lens or dynamic eye concept is
the correct (most accurate) theory for the long-term growth of the
eye.
We have limited resources to deal with the problem. We
should not divide our efforts. Either the plus lens is or is not
effective in halting the movement towards myopia.
An effort to prevent myopia should produce clear results that
allow us to conclude:
1. The plus lens is effective, and because of its demonstrated
effectiveness, its use will be continued on a permanent basis.
2. There is absolutely no possibility that the plus lens has any
effect on a developing case of nearsightedness. The
predictive accuracy of a negative-lens theory is an order of
magnitude more accurate than the predictive accuracy of a
dynamic theory.
A PHYSIOLOGICAL MODEL FOR DEMONSTRATION
In order to explain the eye's dynamic action with clarity, it
would be reasonable to build either an electronic or mechanical
analog of this system. The building of a dynamic model is an
option which could be pursued after the start of the
nearsightedness prevention program.
REFERENCES
1. Young, F. THE EFFECT OF RESTRICTED VISUAL SPACE ON THE
PRIMATE EYE. American Journal of Ophthalmology, Volume 52,
N.5, Part II (11/61)
2. Brown, 0. Young, F,, THE RESPONSE OF A SERVO CONTROLLED EYE
TO A CONFINED VISUAL ENVIRONMENT. The 18th Annual Rocky
Mountain Bioengineering Symposium. Laramie, Wyoming (4/81)
3. Hayden, R. DEVELOPMENT AND PREVENTION OF MYOPIA AT THE UNITED
STATES NAVAL ACADEMY Archives of Ophthalmology Volume 25,
(4/41)
4. Young, F. et al, THE TRANSMISSION OF REFRACTIVE ERRORS WITHIN
ESKIMO FAMILIES Am. J. Optometry. & Arch. Am. Acad.
Optometry., 49 (9): 675-685, 1969
5. Brown, 0. Young, F. THE EYE'S SERVO RESPONSE TO A CONVEX
LENS The 10th Annual Northeast Bioengineering Conference
(Submitted for publication) (4/82)
6. Brown, 0. Young, F. Berger, R, MEASURING THE EYE'S FOCAL
ACCURACY: A HEURISTIC APPROACH, The 3rd Annual Conference of
the IEEE Engineering in Medicine & Biology Society (9/81)
7. Gmelin, R. T., MYOPIA AT WEST POINT: PAST AND PRESENT,
Military Medicine 141 (8) 542-3 (Aug 76) (Measurements made
over a 4 year period indicate that the average movement
towards and into nearsightedness is -1.37 diopters, with a
range of -1.12 to -1.69 diopters.)
cc:
Dr. Karel Montor
Director: Division of Applied Sciences
Chauvenet Hall
The United States Naval Academy
Annapolis, Maryland 21402